Analysis of mid-infrared spectral characteristics of rock outcrops and an evaluation of the kahle model in predicting outcrop thermal inertias

Abstract

This paper summarizes the results of an analysis of emissive spectra acquired at wavelengths of 8.2–13.6μm from multiple targets on granite, amphibolite, and calcareous marble outcrops in the Clare River synform near Tweed, Ontario. Prominent spectral features are noted for all three rock types. The effects of surface contaminants such as lichens are examined. Results indicate that many of the diagnostic spectral features in granite, although damped, remain apparent in surfaces with as much as 71% lichen cover. Cloud cover is also shown to have a significant damping effect on the emissive spectrum. Spectral measurements were carried out in support of an experiment to investigate the accuracy with which the Kahle (1977) numerical model can be used to predict the thermal inertia of rock outcrops in situ. Diurnal surface temperature differences were computed from emission spectra of selected targets on each rock outcrop. The surface temperatures, as well as meteorological data, were inputs to the model. Predicted values from the model were then compared against measured thermal inertias from rock cores removed from each spectral target. Results indicate a mean overestimate in the model's thermal inertia of 25%. A major contributing factor may be inherent errors in the model itself. The model is shown to be quite sensitive to errors in the estimate of the surface albedo, as well as the diurnal range in surface temperature.